U.S. patent application number 10/391729 was filed with the patent office on 2004-01-01 for apparatus and method for producing a small spot of optical energy.
This patent application is currently assigned to Seagate Technology LLC. Invention is credited to Challener, William Albert, Mihalcea, Christophe Daniel, Rausch, Tim.
Application Number | 20040001394 10/391729 |
Document ID | / |
Family ID | 30003230 |
Filed Date | 2004-01-01 |
United States Patent
Application |
20040001394 |
Kind Code |
A1 |
Challener, William Albert ;
et al. |
January 1, 2004 |
Apparatus and method for producing a small spot of optical
energy
Abstract
An apparatus for producing a small spot of optical energy
comprises a planar waveguide shaped to direct a linearly polarized
electromagnetic wave to a focal point within the waveguide, and a
metallic pin positioned at the focal point whereby the linearly
polarized electromagnetic wave creates surface plasmons on a
surface of the pin. The apparatus can further comprise means for
phase shifting a portion of the linearly polarized electromagnetic
wave. Recording heads comprising a magnetic write pole, a planar
waveguide positioned adjacent to the magnetic write pole, the
planar waveguide being shaped to direct a linearly polarized
electromagnetic wave to a focal point within the waveguide, and a
metallic pin positioned at the focal point whereby the linearly
polarized electromagnetic wave creates surface plasmons on a
surface of the pin, and disc drives that use such recording heads
are also disclosed.
Inventors: |
Challener, William Albert;
(Sewickley, PA) ; Mihalcea, Christophe Daniel;
(Pittsburgh, PA) ; Rausch, Tim; (Gibsonia,
PA) |
Correspondence
Address: |
Robert P. Lenart
Pietragallo, Bosick & Gordon
One Oxford Centre, 38th Floor
301 Grant Street
Pittsburgh
PA
15219
US
|
Assignee: |
Seagate Technology LLC
920 Disc Drive
Scotts Valley
CA
95066
|
Family ID: |
30003230 |
Appl. No.: |
10/391729 |
Filed: |
March 19, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60392167 |
Jun 28, 2002 |
|
|
|
60414968 |
Sep 30, 2002 |
|
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|
Current U.S.
Class: |
369/13.32 ;
369/112.27; G9B/5.024; G9B/5.04 |
Current CPC
Class: |
G11B 5/012 20130101;
G11B 5/127 20130101; G11B 2005/0021 20130101; G11B 2005/0005
20130101 |
Class at
Publication: |
369/13.32 ;
369/112.27 |
International
Class: |
G11B 011/00; G11B
007/135 |
Goverment Interests
[0002] This invention was made with the United States Government
support under Agreement No. 70NANB1H3056 awarded by the National
Institute of Standards and Technology (NIST). The United States
Government has certain rights in the invention.
Claims
What is claimed is:
1. An apparatus comprising: a planar waveguide shaped to direct a
linearly polarized electromagnetic wave to a focal point within the
waveguide; and a metallic pin positioned at the focal point.
2. The apparatus of claim 1, wherein the waveguide includes edges
for reflecting the electromagnetic wave toward the focal point.
3. The apparatus of claim 2, wherein the edges have a substantially
parabolic shape.
4. The apparatus of claim 3, wherein an end of the waveguide
adjacent to the pin is truncated.
5. The apparatus of claim 1, wherein the planar waveguide forms a
mode index lens.
6. The apparatus of claim 1, wherein the pin extends through an end
of the planar waveguide.
7. The apparatus of claim 1, further comprising means for phase
shifting a portion of the linearly polarized electromagnetic
wave.
8. The apparatus of claim 7, wherein the means for phase shifting
comprises: a layer of material having a first section with a first
refractive index and a second section with a second refractive
index.
9. The apparatus of claim 7, wherein the planar waveguide includes
a core layer and the means for phase shifting comprises: a first
portion of the core layer having a thickness different from a
thickness of a second portion of the core layer.
10. The apparatus of claim 7, further comprising: a cladding layer
positioned adjacent to the planar waveguide; and wherein the means
for phase shifting includes a first portion of the cladding layer
having a thickness different from a second portion of the cladding
layer.
11. The apparatus of claim 7, wherein the means for phase shifting
comprises: a first diffraction grating and a second diffraction
grating, where the first diffraction grating and the second
diffraction grating are offset in a longitudinal direction.
12. The apparatus of claim 1, further comprising: means for
coupling a transverse magnetic polarized electromagnetic wave into
the planar waveguide.
13. The apparatus of claim 12, wherein the means for coupling a
transverse magnetic polarized electromagnetic wave into the planar
waveguide comprises a diffraction grating.
14. An apparatus comprising: a pyramidal structure having four
substantially flat sides converging to a point; a first material
lying adjacent to an exterior of each of the sides and having a
first index of refraction; a second material lying adjacent to an
interior of each of the sides and having a second index of
refraction; and a metallic pin positioned adjacent to the
point.
15. The apparatus of claim 14, further comprising: means for phase
shifting a portion of an electromagnetic wave in the structure.
16. An apparatus comprising: a conical structure having a first
refractive index; a layer of material on a surface of the conical
structure, the material having a second refractive index, lower
than the first refractive index; a metal layer positioned on the
layer of material; and a metallic pin positioned adjacent to a
point of the conical structure.
17. A recording head comprising: a magnetic write pole; a planar
waveguide positioned adjacent to the magnetic write pole, the
planar waveguide being shaped to direct a linearly polarized
electromagnetic wave to a focal point within the waveguide; and a
metallic pin positioned at the focal point.
18. The recording head of claim 17, wherein the waveguide includes
edges for reflecting the electromagnetic wave toward the focal
point.
19. The apparatus of claim 18, wherein the edges have a
substantially parabolic shape.
20. The apparatus of claim 19, wherein an end of the waveguide
adjacent to the pin is truncated.
21. The apparatus of claim 17, wherein the planar waveguide forms a
mode index lens.
22. The apparatus of claim 17, wherein the pin extends through an
end of the planar waveguide.
23. The recording head of claim 17, further comprising means for
phase shifting a portion of the linearly polarized electromagnetic
wave.
24. The recording head of claim 23, wherein the means for phase
shifting comprises: a layer of material having a first section with
a first refractive index and a second section with a second
refractive index.
25. The recording head of claim 23, wherein the planar waveguide
includes a core layer and the means for phase shifting comprises: a
first portion of the core layer having a thickness different from a
thickness of a second portion of the core layer.
26. The recording head of claim 23, further comprising: a cladding
layer positioned adjacent to the planar waveguide; and wherein the
means for phase shifting includes a first portion of the cladding
layer having a thickness different from a second portion of the
cladding layer.
27. The recording head of claim 23, wherein the means for phase
shifting comprises: a first diffraction grating and a second
diffraction grating, where the first diffraction grating and the
second diffraction grating are offset in a longitudinal
direction.
28. The recording head of claim 17, further comprising: means for
coupling a transverse magnetic polarized electromagnetic wave into
the planar waveguide.
29. The recording head of claim 28, wherein the means for coupling
a transverse magnetic polarized electromagnetic wave into the
planar waveguide comprises a diffraction grating.
30. A recording head comprising: a magnetic write pole; and a
waveguide positioned adjacent to the magnetic write pole, the
waveguide including a pyramidal structure having four substantially
flat sides converging to a point, a first material lying adjacent
to an exterior of each of the sides and having a first index of
refraction, a second material lying adjacent to an interior of each
of the sides and having a second index of refraction, and a
metallic pin positioned adjacent to the point.
31. The recording head of claim 30, further comprising: means for
phase shifting a portion of an electromagnetic wave prior to
reflection by the sides.
32. A recording head comprising: a magnetic write pole; and a
waveguide positioned adjacent to the magnetic write pole, the
waveguide including a conical structure having a first refractive
index, a layer of material on a surface of the conical structure,
the material having a second refractive index, lower than the first
refractive index, a metal layer positioned on the layer of
material, and a metallic pin positioned adjacent to a point of the
conical structure.
33. A disc drive comprising: means for rotating a storage medium;
and means for positioning a recording head adjacent to a surface of
the storage medium; wherein the recording head comprises a magnetic
write pole, a planar waveguide positioned adjacent to the magnetic
write pole, the planar waveguide being shaped to direct a linearly
polarized electromagnetic wave to a focal point within the
waveguide, and a metallic pin positioned at the focal point.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application claims the benefit of U.S. Provisional
Patent Applications Serial Nos. 60/392,167, filed Jun. 28, 2002,
and 60/414,968, filed Sep. 30, 2002.
FIELD OF THE INVENTION
[0003] This invention relates to optical waveguides, and more
particularly to optical waveguides that can be used in heat
assisted magnetic recording.
BACKGROUND OF THE INVENTION
[0004] Magnetic recording heads have utility in magnetic disc drive
storage systems. Most magnetic recording heads used in such systems
today are "longitudinal" magnetic recording heads. Longitudinal
magnetic recording in its conventional form has been projected to
suffer from superparamagnetic instabilities at high bit
densities.
[0005] Superparamagnetic instabilities become an issue as the grain
volume is reduced in order to control media noise for high areal
density recording. The superparamagnetic effect is most evident
when the grain volume V is sufficiently small that the inequality
K.sub.uV/k.sub.BT>70 can no longer be maintained. K.sub.u is the
material's magnetic crystalline anisotropy energy density, k.sub.B
is Boltzmann's constant, and T is absolute temperature. When this
inequality is not satisfied, thermal energy demagnetizes the stored
bits. Therefore, as the grain size is decreased in order to
increase the areal density, a threshold is reached for a given
material K.sub.u and temperature T such that stable data storage is
no longer feasible.
[0006] The thermal stability can be improved by employing a
recording medium formed of a material with a very high K.sub.u.
However, with the available materials the recording heads are not
able to provide a sufficient or high enough magnetic writing field
to write on such a medium. Accordingly, it has been proposed to
overcome the recording head field limitations by employing thermal
energy to heat a local area on the recording medium before or at
about the time of applying the magnetic write field to the medium.
Heat assisted magnetic recording generally refers to the concept of
locally heating a recording medium to reduce the coercivity of the
recording medium so that the applied magnetic writing field can
more easily direct the magnetization of the recording medium during
the temporary magnetic softening of the recording medium caused by
the heat source. Heat assisted magnetic recording allows for the
use of small grain media, which is desirable for recording at
increased areal densities, with a larger magnetic anisotropy at
room temperature to assure sufficient thermal stability. Heat
assisted magnetic recording can be applied to any type of magnetic
storage media, including tilted media, longitudinal media,
perpendicular media and patterned media. By heating the medium, the
K.sub.u or the coercivity is reduced such that the magnetic write
field is sufficient to write to the medium. Once the medium cools
to ambient temperature, the medium has a sufficiently high value of
coercivity to assure thermal stability of the recorded
information.
[0007] It is believed that reducing or changing the bit cell aspect
ratio will extend the bit density limit. However, different
approaches will likely be necessary to overcome the limitations of
longitudinal magnetic recording.
[0008] An alternative to longitudinal recording that overcomes at
least some of the problems associated with the superparamagnetic
effect is "perpendicular" magnetic recording. Perpendicular
magnetic recording is believed to have the capability of extending
recording densities well beyond the limits of longitudinal magnetic
recording. Perpendicular magnetic recording heads for use with a
perpendicular magnetic storage medium may include a pair of
magnetically coupled poles, including a main write pole having a
relatively small bottom surface area and a flux return pole having
a larger bottom surface area. A coil having a plurality of turns is
located adjacent to the main write pole for inducing a magnetic
field between the pole and a soft underlayer of the storage media.
The soft underlayer is located below the hard magnetic recording
layer of the storage media and enhances the amplitude of the field
produced by the main pole. This, in turn, allows the use of storage
media with higher coercive force, consequently, more stable bits
can be stored in the media. In the recording process, an electrical
current in the coil energizes the main pole, which produces a
magnetic field. The image of this field is produced in the soft
underlayer to enhance the field strength produced in the magnetic
media. The flux density that diverges from the tip into the soft
underlayer returns through the return flux pole. The return pole is
located sufficiently far apart from the main write pole such that
the material of the return pole does not affect the magnetic flux
of the main write pole, which is directed vertically into the hard
layer and the soft underlayer of the storage media.
[0009] When applying a heat or light source to the medium, it is
desirable to confine the heat or light to the track where writing
is taking place and to generate the write field in close proximity
to where the medium is heated to accomplish high areal density
recording. In addition, for heat assisted magnetic recording (HAMR)
one of the technological hurdles to overcome is to provide an
efficient technique for delivering large amounts of light power to
the recording medium confined to spots of, for example, 50 nm or
less. A variety of transducer designs have been proposed and some
have been experimentally tested. Among these are metal coated glass
fibers and hollow pyramidal structures with metal walls. For all
these approaches, confinement of the light depends on an aperture
which is to be fabricated into the end of the structure and gives
this kind of transducer the name "aperture probes." Generally these
devices suffer from very low light transmission rendering the
devices useless for HAMR recording. For example, tapered and
metallized optical fibers have demonstrated light confinement down
to approximately 50 nm with a throughput efficiency of 10.sup.-6.
Pyramidal probes made from anisotropic etching of Si wafers have
been designed with throughput efficiencies of 10.sup.-4 for similar
spot sizes. Although this is the state of the art, it is still
about two orders of magnitude too small for HAMR.
[0010] Improvements in throughput efficiency have been achieved for
these transducers by changing the taper angles, filling the hollow
structures with high index materials, and by trying to launch
surface plasmons (SP) on integrated edges and corners of these
tip-like structures. Although doing so does increase the throughput
to some extent, the most promising SP approach is still very
inefficient due to a lack of an efficient SP launching technique.
In addition, all aperture probes suffer from a lower limit on spot
size which is twice the skin depth of the metal film used to form
the aperture. Even for aluminum, the metal with the smallest skin
depth for visible light, this corresponds to a spot size of
.about.20 nm.
[0011] Solid immersion lenses (SILs) and solid immersion mirrors
(SIMs) have also been proposed for concentrating far field optical
energy into small spots. The optical intensity is very high at the
focus but the spot size is still determined by the diffraction
limit which in turn depends on the refractive index of the material
from which the SIL or SIM is made. The smallest spot size which can
be achieved with all currently known transparent materials is
.about.60 nm, which is too large for HAMR.
[0012] A metallic pin can be used as a transducer to concentrate
optical energy into arbitrarily small areal dimensions. The
metallic pin supports a surface plasmon mode which propagates along
the pin, and the width of the external electric field generated by
the surface plasmon mode is proportional to the diameter of the
pin. Smaller pin diameters result in smaller spots, and in
principle the spot size can be made arbitrarily small. However,
smaller pin diameters also result in much shorter propagation
lengths for energy transport. In fact, for a 50 nm spot size the
1/e propagation length of the surface plasmon is typically
substantially less than a micron. Therefore, a metallic pin by
itself is not useful as a near field transducer.
[0013] There is a need for transducers that can provide a reduced
spot size and increased throughput efficiencies.
SUMMARY OF THE INVENTION
[0014] This invention provides an apparatus for producing a small
spot of optical energy comprising a planar waveguide shaped to
direct a linearly polarized electromagnetic wave to a focal point
within the waveguide, and a metallic pin positioned at the focal
point whereby the electromagnetic wave creates surface plasmons on
a surface of the pin.
[0015] The waveguide can include edges that are shaped to reflect
the electromagnetic wave. The edges can have a substantially
parabolic shape. The end of the waveguide can be truncated. The
planar waveguide can alternatively include a mode index lens for
directing the electromagnetic wave to the focal point. The metallic
pin can be embedded in the waveguide and can extend through an end
of the waveguide.
[0016] The apparatus can further comprise means for coupling a
linearly polarized electromagnetic wave into the planar waveguide,
and the means for coupling a linearly polarized electromagnetic
wave into the planar waveguide can comprise a diffraction
grating.
[0017] The apparatus can further comprise means for phase shifting
a portion of the linearly polarized electromagnetic wave. The means
for phase shifting can comprise a layer of material having a first
section with a first refractive index and a second section with a
second refractive index.
[0018] The planar waveguide can include a core layer and the means
for phase shifting can comprise a first portion of the core layer
having a thickness different from a second portion of the core
layer.
[0019] The means for phase shifting can alternatively comprise a
first diffraction grating and a second diffraction grating, where
the first diffraction grating and the second diffraction grating
are offset in a longitudinal direction.
[0020] The apparatus can further include a cladding layer adjacent
to one or both sides of the planar waveguide. The cladding layer
can have different thicknesses to provide means for phase shifting
the electromagnetic wave.
[0021] In another aspect the invention can include a means for
coupling a linearly polarized electromagnetic wave into the planar
waveguide to excite a transverse magnetic waveguide mode.
Furthermore, the waveguide thickness can be chosen to be slightly
greater than the waveguide cutoff thickness for the transverse
magnetic mode.
[0022] In another aspect, the invention encompasses an apparatus
comprising a pyramidal structure having four substantially flat
sides converging to a point, a first material lying adjacent to an
exterior of each of the sides and having a first index of
refraction, a second material lying adjacent to an interior of each
of the sides and having a second index of refraction, and a
metallic pin positioned adjacent to the point. The apparatus can
further include means for phase shifting a portion of an
electromagnetic wave prior to reflection by the sides.
[0023] The invention further encompasses an apparatus comprising a
conical structure having a first refractive index, a layer of
material on a surface of the conical structure, the material having
a second refractive index lower than the first refractive index, a
metal layer positioned on the layer of material, and a metallic pin
positioned adjacent to a point of the conical structure.
[0024] The invention also encompasses a recording head comprising a
magnetic write pole, a planar waveguide positioned adjacent to the
magnetic write pole, the planar waveguide shaped to direct a
linearly polarized electromagnetic wave to a focal point within the
waveguide, and a metallic pin positioned at the focal point whereby
the electromagnetic wave creates surface plasmons on a surface of
the pin.
[0025] The invention further encompasses a recording head
comprising a magnetic write pole, and a waveguide positioned
adjacent to the magnetic write pole, the waveguide including a
pyramidal structure having four substantially flat sides converging
to a point, a first material lying adjacent to an exterior of each
of the sides and having a first index of refraction, a second
material lying adjacent to an interior of each of the sides and
having a second index of refraction, and a metallic pin positioned
adjacent to the point.
[0026] Another aspect of the invention encompasses a recording head
comprising a magnetic write pole, and a waveguide positioned
adjacent to the magnetic write pole, the waveguide including a
conical structure having a first refractive index, a layer of
material on a surface of the conical structure, the material having
a second refractive index, lower than the first refractive index, a
metal layer positioned on the layer of material, and a metallic pin
positioned adjacent to a point of the conical structure.
[0027] The invention further encompasses a disc drive comprising
means for rotating a storage medium, and means for positioning a
recording head adjacent to a surface of the storage medium, wherein
the recording head comprises a magnetic write pole, a planar
waveguide positioned adjacent to the magnetic write pole, the
planar waveguide being shaped to direct a linearly polarized
electromagnetic wave to a focal point within the waveguide, and a
metallic pin positioned at the focal point whereby the
electromagnetic wave creates surface plasmons on a surface of the
pin.
BRIEF DESCRIPTION OF THE DRAWINGS
[0028] FIG. 1 is a pictorial representation of a magnetic disc
drive that can include magnetic heads constructed in accordance
with this invention.
[0029] FIG. 2 is a schematic representation of a planar waveguide
constructed in accordance with this invention.
[0030] FIG. 3 is a schematic representation of another planar
waveguide constructed in accordance with this invention.
[0031] FIG. 4 is a schematic representation of another planar
waveguide constructed in accordance with this invention.
[0032] FIG. 5 is a schematic representation of two diffraction
gratings.
[0033] FIG. 6 is a graph of thickness vs. effective index.
[0034] FIG. 7 is a schematic representation of another planar
waveguide constructed in accordance with this invention.
[0035] FIG. 8 is a schematic representation of a TE mode wave in a
waveguide.
[0036] FIG. 9 is a schematic representation of a TM mode wave in a
waveguide.
[0037] FIG. 10 is a schematic illustration of radial polarization
in an electromagnetic wave.
[0038] FIG. 11 is a schematic representation of a composite wave
plate for generating radial polarization.
[0039] FIG. 12 is a schematic representation of pseudo-radial
polarization for the light transmitted by the waveplate.
[0040] FIG. 13 is a schematic illustration of a radially polarized
beam incident upon a solid immersion lens.
[0041] FIG. 14 is a graph of spot diameter vs. core diameter.
[0042] FIG. 15 is a graph of beam diameter vs. propagation
distance.
[0043] FIG. 16 is a schematic representation of a conical
transducer constructed in accordance with this invention.
[0044] FIG. 17 is a schematic representation of a pyramidal
transducer constructed in accordance with this invention.
[0045] FIG. 18 is a schematic representation of a recording head
including the waveguide of this invention.
[0046] FIG. 19 is a schematic representation of a truncated solid
immersion mirror constructed in accordance with this invention.
[0047] FIG. 20 is a schematic representation of another truncated
solid immersion mirror constructed in accordance with this
invention.
[0048] FIG. 21 is an isometric view of another waveguide
constructed in accordance with this invention.
[0049] FIG. 22 is a side elevation view of another waveguide
constructed in accordance with this invention.
DETAILED DESCRIPTION OF THE INVENTION
[0050] This invention encompasses devices that can be used in
magnetic and optical recording heads for use with magnetic and/or
optical recording media, as well as magnetic and/or optical
recording heads that include such devices and disc drives that
include the recording heads. FIG. 1 is a pictorial representation
of a disc drive 10 that can utilize recording heads constructed in
accordance with this invention. The disc drive includes a housing
12 (with the upper portion removed and the lower portion visible in
this view) sized and configured to contain the various components
of the disc drive. The disc drive includes a spindle motor 14 for
rotating at least one data storage medium 16 within the housing, in
this case a magnetic disc. At least one arm 18 is contained within
the housing 12, with each arm 18 having a first end 20 with a
recording and/or reading head or slider 22, and a second end 24
pivotally mounted on a shaft by a bearing 26. An actuator motor 28
is located at the arm's second end 24, for pivoting the arm 18 to
position the head 22 over a desired sector of the disc 16. The
actuator motor 28 is regulated by a controller that is not shown in
this view and is well known in the art.
[0051] For heat assisted magnetic recording, an electromagnetic
wave of, for example, visible or ultraviolet light is directed onto
a surface of a data storage medium to raise the temperature of the
localized area of the medium to facilitate switching of the
magnetization of the area. Well known solid immersion lenses (SILs)
have been proposed for use in reducing the size of a spot on the
medium that is subjected to the electromagnetic radiation. In
addition, solid immersion mirrors (SIMs) have been described in the
literature. SILs and SIMs may be either three-dimensional or
two-dimensional. In the latter case they correspond to mode index
lenses or mirrors in planar waveguides. A metallic pin can be
inserted at the focus of a SIM to guide a confined beam of light
out of the SIM to the surface of the recording medium. This
invention provides an efficient means of coupling light from the
SIM (or SIL) into the metallic pin.
[0052] Two-dimensional planar waveguides can be used to generate
focused beams by means of mode index lenses or planar solid
immersion mirrors. FIG. 2 is a schematic representation of a
two-dimensional waveguide 30 in the form of a solid immersion
mirror, including a metallic pin 32 embedded in an end of the
waveguide. The tip 34 of the pin extends beyond the waveguide. The
waveguide includes edges 36, 38 having a substantially parabolic
shape in the example shown in FIG. 2. Due to differences in
refractive index between the waveguide and the adjacent material,
an electromagnetic wave traveling in the axial direction through
the waveguide as illustrated by arrows 40 and 42 would be reflected
by the waveguide onto the surface of the metallic pin. If the
electric field at the focal point is parallel to the axis of the
pin then it can couple to the pin and generate surface plasmons
along the surface of the pin. Near field radiation then emanates
from the tip of the pin as illustrated by arrows 44. The metallic
pin placed at the focus concentrates the light to a much smaller
spot than would be possible with a mode index lens or SIM alone.
The waveguide can be truncated at the end 46 adjacent to the pin so
that most of the incoming electromagnetic wave strikes the edges of
the waveguide at an angle less than some predetermined angle, such
as 45.degree.. For a linearly polarized collimated electromagnetic
wave, edges having a parabolic shape will focus the wave to a focal
point. However, it should be understood that other edge shapes can
be used if the incoming wave is conditioned such that the
combination of the wave characteristics and the edge shape result
in the desired focusing of the wave at the pin. The pin can have a
rectangular cross-section and can be tapered to a point. However,
pins having other cross-sectional shapes can also be used.
[0053] The waveguide can be made of, for example, a high index
dielectric core material like TiO.sub.2, Ta.sub.2O.sub.5, Si, SiN,
or ZnS depending on the wavelength and refractive index desired.
For example, Si has a very large index of 3.5 at a wavelength of
1550 nm in the near infrared, but it is not transparent to visible
light. Ta.sub.2O.sub.5 has a lower index of about 2.1, but is
transparent throughout the near infrared and visible. The waveguide
also contains dielectric cladding layers on either side of the
core. The cladding layer must have a lower refractive index than
the core layer. Preferably the difference in refractive index
between the core and cladding should be as large as possible. Air
is a suitable dielectric for one side of the cladding. Other
dielectrics that could be used as cladding layers include SiO.sub.2
with an index of 1.5 and Al.sub.2O.sub.3 with an index of about
1.8.
[0054] When the invention is used with a transverse electric (TE)
mode electromagnetic wave, means can be provided to phase shift a
portion of the electromagnetic wave. This phase shift can be
achieved by providing a means for launching the two-dimensional
analog of a radially polarized wave into the planar waveguide. We
term this a split linear polarization waveguide mode. Two methods
are described below for achieving the split linear polarization.
The first technique modifies half of the planar waveguide by
changing the refractive index of the core or cladding dielectrics
and/or the thickness of the core or cladding dielectrics in the
waveguide in one section as shown in the FIG. 3. The planar
waveguide 50 of FIG. 3 includes a first section 52 of the core
dielectric having an effective index of refraction of n.sub.1
(which is a function of the index of refraction and thickness of
all core and cladding layers in the waveguide), and a second
section 54 of the core dielectric having an effective index of
refraction of n.sub.2. The length of section 54 in an axial
direction is designated as d.sub.1. Light enters the waveguide as
illustrated by arrows 56 and 58. The incident light is linearly
polarized in the plane of the waveguide. Arrows 60, 62, 64, 66, 68
and 70 illustrate the electric field of the incident light. Arrows
60 and 62 show that the electric field component of the incident
light initially lies in the plane of the waveguide for transverse
electric polarization. Section 54 of the waveguide causes a
differential phase shift between the waveguide mode in the two
halves of the waveguide such that the electromagnetic field of
light exiting section 54, as illustrated by arrow 66, is
180.degree. out of phase with respect to light passing through
section 52, as illustrated by arrow 64. As the light is reflected
at the edges of the waveguide, the reflected waves illustrated by
arrows 72 and 74 have electric fields as illustrated by arrows 68
and 70 that include both longitudinal and transverse components in
the case of TE polarization. Where the reflected waves meet, the
transverse components cancel, leaving the longitudinal components
that add to produce an electric field that is axially aligned with
the waveguide and used to excite surface plasmons on the metal tip
76. This axial field is desirable to improve the fraction of energy
that exits the waveguide.
[0055] The time required for the electromagnetic wave to propagate
through a section of waveguide is determined by the effective
refractive index and length of the section. The refractive index
and length can be chosen so that there is a net phase shift of
180.degree. between the wave propagating through the first section
and the wave propagating through the second section. This can be
represented by, 1 ( n 1 - n 2 ) d = 2 ( 1 )
[0056] where n.sub.1 and n.sub.2 are the effective refractive
indices of the TE waveguide mode in the first and second sections,
d is length of the second section, and .lambda. is the wavelength
of the incident electromagnetic radiation. The effective refractive
index is a function of the core and cladding refractive indices and
thicknesses as well as the polarization state. There are many ways
to get the index change n.sub.2 with respect to FIG. 3. For
example, the index can be changed by varying the thickness of the
waveguide, using ion implantation, or strip loading the waveguide
with a metal, etc.
[0057] Referring to the structure of FIG. 3, if we assume that the
planar waveguide is comprised of Ta.sub.2O.sub.5 with a thickness
of 200 nm, then the required length for the modified section is
shown by line 122 of the graph of FIG. 6, a function of
Ta.sub.2O.sub.5 film thickness. For example, a Ta.sub.2O.sub.5 film
with a thickness of 100 nm would have an effective index of 1.76
and the section length 54 should be about 1.2 .mu.m long in order
to generate a net phase shift of 180.degree.. Alternatively, the
entire waveguide could start with a Ta.sub.2O.sub.5 thickness of
100 nm, and a 1.2 .mu.m long modified section 54 of 200 nm thick
Ta.sub.2O.sub.5 could be used instead. This would also generate a
180.degree. phase shift.
[0058] An alternative technique for generating a split linearly
polarized planar waveguide mode makes use of a diffraction grating
to launch the planar mode, as illustrated in FIG. 4. FIG. 4 shows a
two-dimensional waveguide 80 in the form of a solid immersion
mirror, including first and second diffraction gratings 82 and 84.
Diffraction gratings are commonly used to inject light into a
planar waveguide. To generate split linear polarization the two
diffraction gratings 82 and 84 are used with a longitudinal offset
between them as shown in FIG. 4. The diffraction gratings are
offset by a distance d.sub.2.
[0059] The purpose of the dual grating is to introduce a relative
180.degree. phase shift between the two halves of the beam. Arrows
86 and 88 illustrate an incident electromagnetic wave having an
electric field represented by arrows 90, 92, and a transverse
electric waveguide mode having an electric field represented by
arrows 94, 96, 98 and 100. As shown by arrows 90 and 92, the
electric field of the incident wave is initially linearly polarized
in the plane of the waveguide for TE modes. Grating 82 is used to
launch the wave into one half of the waveguide. Grating 84 is used
to launch the wave into the other half of the waveguide. The
longitudinal offset in the position of the two gratings causes a
180.degree. phase shift to occur between the two waveguide modes as
shown by arrows 94 and 96. After reflection from the edges 102 and
104 of the waveguide, the reflected waves as illustrated by arrows
106 and 108 have electric fields that include both longitudinal and
transverse components in the case of TE polarization. When the
reflected waves meet at the focal point, the transverse components
of the electric fields cancel and the longitudinal components of
the electric fields add. This excites surface plasmons on the
metallic pin 110. The offset between the gratings is given by the
formula: 2 offset = 2 ( n eff - n inc sin ) ( 2 )
[0060] where .theta. is the angle of incidence, n.sub.eff is the
effective index of refraction for the waveguide mode, and n.sub.inc
is the refractive index of the incident medium. As shown in FIG. 5
the incident collimated laser beam reaches the end of the first
portion of the waveguide before it reaches the end of the second
portion of the waveguide. The time difference is: 3 t 1 = n inc d
sin c . ( 3 )
[0061] At the end of the first grating the waveguide mode begins
propagating with a phase velocity of 4 v p = c n eff . ( 4 )
[0062] It reaches the end of the second grating after the interval
5 t 2 = n eff d c . ( 5 )
[0063] The time interval between t.sub.1 and t.sub.2 is sufficient
to generate a 180.degree. phase shift in the propagating waveguide
mode, 6 t 2 - t 1 = d c ( n eff - n inc sin ) = 1 2 f = 2 c . ( 6
)
[0064] This equation reduces to Equation (2).
[0065] The waveguide can be positioned on a surface of a substrate
of, for example, SiO.sub.2. For a waveguide constructed as shown in
FIG. 4, for TE polarization at a wavelength of 400 nm, the
effective index of refraction of a 40 nm Ta.sub.2O.sub.5 waveguide
on an SiO.sub.2 substrate is 1.553. For a 45.degree. angle of
incidence in air of the collimated laser beam onto the waveguide,
the offset should be 236 nm. As a second example, for TE
polarization at a wavelength of 633 nm and a 50 nm Ta.sub.2O.sub.5
waveguide on an SiO.sub.2 substrate the effective index is 1.469,
so the offset should be 415 nm for a 45.degree. angle of incidence
of the laser beam in air. As a third example, for TE polarization
at a 1550 nm wavelength and a 100 nm Si waveguide on an SiO.sub.2
substrate the effective index is 2.129, so the offset should be 545
nm for a 45.degree. angle of incidence of the laser beam in
air.
[0066] FIG. 5 is a schematic representation of the two diffraction
gratings 82 and 84 of FIG. 4. FIG. 5 shows the grating offset and
the incident light represented by arrows 86 and 88.
[0067] FIG. 6 is a graph of the effective index 120 for a waveguide
comprised of a Ta.sub.2O.sub.5 core (n=2.2) sandwiched between
SiO.sub.2 (n=1.5) and air cladding layers at a wavelength of 633 nm
for TE polarization vs. thickness of the waveguide. As the film
gets very thick its effective index approaches that of the bulk
Ta.sub.2O.sub.5, i.e. 2.2. As the film gets very thin, its
effective index drops towards that of the SiO.sub.2 substrate, i.e.
1.5. For film thicknesses below about 40 nm there are no
propagating TE modes.
[0068] Another way of exciting the metallic pin with a strong
z-polarization is to excite a TM mode in the waveguide near the
cutoff dimension of the waveguide rather than the TE mode as
discussed above. A waveguide that uses a TM mode is illustrated in
FIG. 7. The planar waveguide 130 of FIG. 7 includes a layer 132 of
transparent material such as Ta.sub.2O.sub.5 on a surface of a
substrate, such as SiO.sub.2. A single grating 134 is provided for
coupling light into the waveguide. Light enters the waveguide as
illustrated by arrows 136 and 138. The incident light is polarized
in the plane of incidence and perpendicular to the plane of the
waveguide so that the electric field within the waveguide has a
component that lies in the plane of the waveguide along the
direction of propagation as shown by arrows 133 and 135 and another
component that lies perpendicular to both the direction of
propagation and the plane of the waveguide. This is illustrated in
a side view in FIG. 9. The electric field component which lies
along the direction of propagation is E.sub.z, and the electric
field component which is perpendicular to the direction of
propagation and the plane of the waveguide is E.sub.y. After
reflecting from the edge of the waveguide, the electric field
component E.sub.y is unchanged, but the electric field component
E.sub.z is divided into a longitudinal component parallel to the
pin, E.sub.L, and a transverse component, E.sub.T, perpendicular to
the pin. Where the reflected waves 137 and 139 in FIG. 7 meet, the
electric fields add together generating a total electric field
which has one component parallel to the pin, E.sub.L, and another
component perpendicular to both the waveguide and the pin (denoted
by E.sub.y in FIG. 9). The transverse field components, E.sub.T,
cancel. As the thickness of the core is reduced towards the cutoff
thickness, the component E.sub.L of the electric field which lies
parallel to the pin increases relative to the component E.sub.y
that lies perpendicular to both the plane of the waveguide and the
pin. Because the component that lies perpendicular to the pin does
not efficiently couple into the pin, the waveguide should be
designed to operate near its cutoff for which the amplitude of the
electric field component in the plane of the waveguide is maximized
in order to transfer electromagnetic energy most efficiently into
the pin.
[0069] FIG. 8 is a schematic representation of a TE mode wave in a
waveguide. In FIG. 8, an electromagnetic wave 150 is shown within a
waveguide 152. The electromagnetic wave is polarized in the TE mode
such that the electric field is perpendicular to the plane of the
figure and the magnetic field H has components H.sub.y and H.sub.z,
with component H.sub.z lying in a direction parallel to the axis of
the waveguide. The electromagnetic wave can be seen to reflect off
of the sides 154 and 156 as it travels along the waveguide.
[0070] FIG. 9 is a schematic representation of a TM mode wave in a
waveguide. In FIG. 9, an electromagnetic wave 160 is shown within a
waveguide 162. The electromagnetic wave is polarized in the TM mode
such that the magnetic field is perpendicular to the plane of the
figure and the electric field E has components E.sub.y and E.sub.z,
with component E.sub.z lying in a direction parallel to the axis of
the waveguide. The electromagnetic wave can be seen to reflect off
of the sides 164 and 166 as it travels along the waveguide.
[0071] From FIG. 9 it is apparent that for the TM mode, there is a
component of the electric field in the z-direction. The closer the
mode is to cutoff, the stronger the z-component. The TM mode can be
excited by a single grating and does not require the offset grating
shown in FIG. 4. By using a TM mode, the phase shifting means of
FIG. 4 can be eliminated.
[0072] For some transducers it is desirable to use a radially
polarized electromagnetic wave. Radial polarization may be
understood by referring to FIG. 10. A radially polarized
electromagnetic wave includes an electric field component that lies
in a plane 170 that is perpendicular to the direction of travel
represented by a k vector 172, and is represented by arrows 174,
176, 178 and 180.
[0073] The magnetic field, H, for a radially polarized wave is
circumferential with respect to the k vector. Techniques for
generating a radially polarized wave are well known. For example,
two half-wave plates can be cut into quarters 182, 184, 186 and 188
and rearranged into a single wave plate with fast axes as shown in
FIG. 11.
[0074] A half wave plate has the property that it rotates the plane
of polarization by twice the angle of the wave plate. Therefore, if
a plane wave uniformly polarized in the vertical direction is
incident upon the modified wave plate, the transmitted polarization
will be as illustrated by the arrows 190, 192, 194 and 196 in FIG.
12.
[0075] The transmitted polarization has a strong radial component
and a smaller circumferential component. The circumferential
component can be eliminated by focusing the beam through a spatial
pinhole filter which strongly attenuates the circumferential
components relative to the radial components. The result will be a
radially polarized beam as shown in FIG. 10. There are other
methods for generating radially polarized beams as well.
[0076] If this radially polarized beam is incident upon either a
solid immersion lens (SIL) or a solid immersion mirror (SIM) it
will be brought to a focus. FIG. 13 is a schematic representation
of a SIL 200 that is used to focus a radially polarized wave. At
the focus 202, the components of the electric field, illustrated by
arrows 204, 206, tend to cancel leaving only an electric field
component that lies along the axis of propagation 208.
[0077] This axial electric field polarization for either a SIL or a
SIM can be used in combination with a metallic pin 210 at the focus
to provide a reduced size optical spot with improved throughput
efficiency. The pin does not need to be very long, only on the
order of the depth of focus or about a wavelength. The length of
the pin can be optimized to support a resonant mode and radiate
light efficiently from its lower end. The metal pin can support a
surface plasmon resonance propagating along it axially. The field
can be tightly confined by making the diameter of the pin small.
However, as the diameter of the pin is reduced the propagation
length of the SP mode also decreases. For an aluminum pin the
diameter of the spot as a function of the diameter of the pin is
shown in FIG. 14. For a 50 nm spot size the metallic pin should be
about 20 nm in diameter. The data in FIG. 14 is for an infinite
cylindrical pin. For a finite cylinder or a pointed pin, the spot
size will be similar or even smaller.
[0078] The propagation length as a function of pin diameter is
shown in FIG. 15. The propagation length is defined as the distance
for which the amplitude of the wave drops to 1/e of its initial
value. A pin diameter of 20 nm corresponds to a propagation
distance of only 300 nm at a wavelength of 1550 nm. For these
calculations the metal pin is surrounded by a dielectric with
index=2.2.
[0079] In order to allow the SP mode to propagate a longer
distance, the pin could be cone shaped with its point near the
bottom of the SIL or SIM. As the diameter of the pin increases the
propagation length of the SP mode also increases. So energy which
is incident upon the conical pin at the end opposite that of the
point would be able to propagate more easily to the point.
[0080] Different kinds of aperture probes can also be combined with
radially polarized light and a metallic pin transducer to confine
the power. A three-dimensional design is illustrated in FIG. 16.
The structure of FIG. 16 includes a tapered cylindrically symmetric
optical fiber 220 comprising a generally cone shaped section of
high dielectric material 222, and a layer of low dielectric
material 224 on an outer surface of the high dielectric material. A
thin film coating of metal 226 is deposited on the surface of the
low dielectric material. When light enters the structure as shown
by arrows 228 and 230, surface plasmons 232 and 234 are generated
along the interface between the low dielectric material and the
metal layer. The surface plasmons are used to excite a metallic pin
236 that radiates the electromagnetic wave as illustrated by arrows
238. The taper angle is chosen in conjunction with the thin films
to optimally excite the SP mode with collimated and radially
polarized light.
[0081] Another design, illustrated in FIG. 17, is based on
commercially available pyramidal hollow metal aperture probes. To
construct the waveguide of this invention, the fabrication process
must be modified to produce the metallic pin. The structure of FIG.
17 includes a four-sided transparent dielectric pyramid 250 having
a metallic pin 252 located at a tip thereof. The dielectric pyramid
may be composed of a high index dielectric like Ta.sub.2O.sub.5 or
TiO.sub.2 or a low index dielectric like SiO.sub.2 or
Al.sub.2O.sub.3. A second transparent low index dielectric material
indicated by 254 and 256 is coated over the pyramid and metallic
pin. This dielectric material may be SiO.sub.2. The resulting
structure is embedded in a substrate 258. The pin and ends of the
dielectric layers protrude from a surface of the substrate. A layer
260 of metal, such as silver or aluminum, is positioned on the
surface of the substrate and adjacent to the protruding portions of
the dielectric layer 254 and 256. An opening 262 is provided
adjacent to the tip of the metallic pin. A phase shifting element
264 can be included as shown in FIG. 17 to serve the same function
as the phase shifting elements described in FIGS. 3 and 4, that is,
to convert a linearly polarized waveguide mode into a split linear
polarization. Two-dimensional structures such as the waveguide of
FIG. 17 can also be readily fabricated using conventional
micro-electromechanical systems technologies that rely on tapering
rather than on focusing by parabolic or ellipsoidal structures. In
each case, split linearly polarized light or radially polarized
light can be used to effectively launch a SP on the metallic pin
that is to be used to transfer/confine the optical power.
[0082] FIG. 18 is a partially schematic side view of a heat
assisted magnetic recording head 280 and a magnetic recording
medium 282. Although an embodiment of the invention is described
herein with reference to recording head 280 as a perpendicular
magnetic recording head and the medium 282 as a perpendicular
magnetic recording medium, it will be appreciated that aspects of
the invention may also be used in conjunction with other types of
recording heads and/or recording mediums where it may be desirable
to employ heat assisted recording. Specifically, the recording head
280 may include a writer section comprising a main write pole 284
and a return or opposing pole 286 that are magnetically coupled by
a yoke or pedestal 288. It will be appreciated that the recording
head 280 may be constructed with a write pole 284 only and no
return pole 286 or yoke 288. A magnetization coil 290 surrounds the
yoke or pedestal 288 for energizing the recording head 280. The
recording head 280 also may include a read head, not shown, which
may be any conventional type read head as is generally known in the
art. The waveguide can alternatively be positioned on the other
side of the pole. In another example, the pin and the pole can be
the same material, in which case the pin can function as both the
electromagnetic transducer and the source of the field.
[0083] Still referring to FIG. 18, the recording medium 282 is
positioned adjacent to or under the recording head 280. The
recording medium 282 includes a substrate 292, which may be made of
any suitable material such as ceramic glass or amorphous glass. A
soft magnetic underlayer 294 may be deposited on the substrate 292.
The soft magnetic underlayer 294 may be made of any suitable
material such as, for example, alloys or multilayers having Co, Fe,
Ni, Pd, Pt or Ru. A hard magnetic recording layer 296 is deposited
on the soft underlayer 294, with the perpendicular oriented
magnetic domains contained in the hard layer 296. Suitable hard
magnetic materials for the hard magnetic recording layer 296 may
include at least one material selected from, for example, FePt or
CoCrPt alloys having a relatively high anisotropy at ambient
temperature.
[0084] The recording head 280 also includes a planar waveguide 298
that directs light received from a light source onto a surface of a
recording medium to heat the magnetic recording medium 282
proximate to where the write pole 284 applies the magnetic write
field H to the recording medium 282. The planar waveguide includes
a light transmitting layer 300. The optical waveguide 298 acts in
association with a light source 302 which transmits light, for
example via an optical fiber 304, that is coupled to the optical
waveguide 298, by a coupling means such as a grating 306. The light
source 302 may be, for example, a laser diode, or other suitable
laser light sources. This provides for the generation of a guided
mode that may propagate through the optical waveguide 298 toward
the recording medium. EM radiation, generally designated by
reference number 310, is transmitted from the waveguide 298 for
heating the recording medium 282, and particularly for heating a
localized area 312 of the recording layer 296.
[0085] The optical waveguide 298 can be constructed in accordance
with any of the waveguides set forth in FIGS. 2, 3, 4, 7, 16 or
17.
[0086] The waveguides of this invention can also be used in optical
recording applications in which either a magnetic field is not
needed, such as write once and phase change recording, or where an
external magnet could be positioned below the substrate, such as in
magneto-optic recording. Alternatively, these structures could
potentially be useful in a probe storage application.
[0087] This invention also encompasses three-dimensional waveguides
as illustrated in FIGS. 19 and 20. FIG. 19 is a schematic
representation of a truncated solid immersion mirror 320
constructed in accordance with this invention. Electromagnetic
waves enter the SIM as illustrated by arrows 322 and 324 and are
reflected off of the sides as illustrated by arrows 326 and 328.
This focuses the light at a focal point 330. The focal point is
positioned adjacent to a truncated edge 332 of the SIM.
[0088] FIG. 20 is a schematic representation of another truncated
solid immersion mirror 334 constructed in accordance with this
invention. Electromagnetic waves enter the SIM as illustrated by
arrows 336 and 338 and are reflected off of the sides as
illustrated by arrows 340 and 342. This focuses the light at a
focal point 344. The focal point is positioned adjacent to a
truncated edge 346 of the SIM. A focusing means 348 is positioned
to focus electromagnetic waves that enter near the center of the
input edge of the SIM, as illustrated by arrows 350, 352 and
354.
[0089] The SIMs of FIGS. 19 and 20 use total internal reflection to
direct the light rays from an incident collimated beam of light
towards a focal point at the bottom surface of the SIM. Because all
of the rays converge within the high index medium of the SIM, the
minimum spot size is equivalent to that of a solid immersion lens.
However, there are no longer practical difficulties in feeding the
SIM or mounting the SIM, so the minimum spot size realized in
practice is much closer to the theoretical limit.
[0090] The structures of FIGS. 19 and 20 are truncated solid
immersion mirrors in which there is no refraction except at the top
lens surface in FIG. 20, but instead, rays are redirected by total
internal reflection to the focus of the mirror. Light rays which
enter a parabolic mirror parallel to the optical axis of the
parabola are brought into focus at the focal point of the parabola
as shown in FIGS. 19 and 20. The truncated parabolic lens is made
of a material which has a high index of refraction compared to the
surrounding medium. The lens is truncated at a plane which cuts
through the focal point of the lens. The maximum angle of incidence
of the marginal ray on the parabolic surface varies. In the
embodiment of FIG. 19 it is 450. In order to ensure total internal
reflection for all rays in the incident beam, the critical angle
equation must be satisfied as follows.
n.sub.med=n.sub.SH sin 6.sub.max={square root}{square root over
(2)}.multidot.n.sub.SH. (7)
[0091] If the SIM is made of glass with an index of refraction of
1.5, then the surrounding medium can be air, with N=1, and all
light rays striking the parabolic curve of the SIM will be totally
reflected. In order to efficiently reflect light rays incident
below the critical angle, the surface of the SIM in the region
below the critical angle would need to be coated with a metallic
reflector like silver or aluminum.
[0092] There is a region in the center of the embodiment of FIG. 19
where incident light does not contribute to the focused spot. It is
possible to shape the top surface of the SIM, or to affix a second
piano-convex lens to this surface, to also focus these rays as
shown in FIG. 20. However, these low angle rays are not as
important for generating a small focused spot. The SIM can also be
fabricated from a material with a graded refractive index in the
radial direction to both focus the light in the center region of
the SIM and to reduce the critical angle required for total
internal reflection. However, doing this would make the SIM
dispersive and monochromatic light would be required.
[0093] The truncated parabolic SIM design can be easily mounted at
its top edge without interfering with the incident high angle rays.
The lens should be essentially achromatic because the light rays
are reflected rather than refracted (except for the top surface
plano-convex lens if present), and the angle of reflection is
independent of wavelength or refractive index. Finally, another
advantage of this design is that often the incident collimated beam
has a Gaussian intensity profile. In a conventional SIL design, the
outer highest angle light rays which are the most important for
generating the smallest spot size are generated from the edges of
the Gaussian beam with the lowest intensity. In this parabolic SIM
design, however, the highest angle rays reflected to the focal
point come from nearer to the center of the incident beam and,
therefore, will have a higher intensity.
[0094] It is also possible that the waveguide can include only one
parabolic edge and another edge that is a different shape, such as
straight. This structure could enable some head geometries that
might be more amenable to fabrication.
[0095] FIG. 21 is an isometric view of another waveguide 360
constructed in accordance with this invention. Waveguide 360
includes a core layer 362 having a first portion 364 of a first
thickness and a second portion 366 of a second thickness and shaped
to form a mode index lens 368. A cladding layer 370 is positioned
adjacent to one side of the waveguide. A pin 372 is positioned at
the focal point of the mode index lens.
[0096] FIG. 22 is a side elevation view of another waveguide 374
constructed in accordance with this invention. Waveguide 374
includes a core layer 376 and a cladding layer 378 is positioned
adjacent to one side of the waveguide. The thickness of the
cladding layer can be varied to provide a means for phase shifting
the electromagnetic wave in the waveguide. Pin 380 is positioned at
the focal point of the waveguide. It should be recognized that the
cladding layer can be positioned on either one side or both sides
of the core layer.
[0097] While the present invention has been described in terms of
several examples, it will be apparent to those skilled in the art
that various changes can be made to the disclosed examples without
departing from the scope of the invention as defined by the
following claims.
* * * * *